I found a neutral density filter amoung my photo gear today and it fits the 43mm threads on my Zeiss 35mm f2 Biogon. The M10’s shutter tops out at 1/4000 of a second which is only limiting when you want to shoot wide open in bright sunlight. I took it out for a test drive this evening and it worked great. Most of these shots are at f2 but I did remove the filter towards the end of the walk as the sun getting lower in the sky!
Leica M10 & 35mm Zeiss Biogon f2 lens